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Old 08-01-2007, 01:30   #1
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fairing

now i have been using epoxy mixed with qcell, the problem is that once you have sanded it down, you cant seem to put another layer of qcell epoxy over the top, the reason being that all the resin sinks through the qcell and sits on top of the previous layer and creates a hard spot, when you go to resand the sandpaper sands all the soft stuff around the resin creating a horrible hard spot so waht do you do, i know people that build stripplank boats do a lot of fairing so what is the secret??
sean
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Old 08-01-2007, 02:08   #2
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You may be doing a couple of things wrong.
1: Filling to deep an area causing the epoxy mix to heat. When it heats, the epoxy can seperate out of the filler.
2: You have too sloppy a mix. You need to put in more filler.
3: You are not using the correct filler powder for fairing. I am not sure what you guy's call "Q-Cell". There are several types of powders available, but three main types of uses basicaly put all powders into three catergories.
A: Glue powder, which is "fumed Silica" or "coloidial silica". This product is a thixotropic substance when mixed with epoxy. It can be used on it's own making a glue. Different consistancies can make glues for different uses. From laminating through the thicker gap filling glues. It should NOT be used on it's own as fairing compound as it goes as hard as hobnails and sanding is very difficult. There are other powders used for glue making, but the silica is now considered the better more modern additive
B: Microspheres. These are exactly as their name emplies and are an open cell sphere. They are used as a cheaper filler/fairing compound above waterline. It is important to add an amount of Silica powder to this mix to create the "thixotropic" characteristic required to sustain the epoxy in better mix suspention. How much the ratio will determin the use as a filler or fairing compound. Fairing needs to be a very thick consitancy. This aids sanding. This mix is normally used above waterline as it can absorb water.
C: Micro Balloons. This powder is a closed cell balloon. Extremely lightweight and because of being a closed cell, they will not absorb anywater. This makes them the best for below waterline. It also is the easiest of all the powders to sand, making fairing easy. Unfortunately it is expensive.
Does that help??
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Old 08-01-2007, 06:34   #3
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ok i mix it thick enough that i can handle it without gloves and not get resin on my hands(like play dough and a bitch to trowel) i have played weith differnet consistencies and for vertical work i use it like this but for flat surfaces a little runnier, no matter how thick i mix it there is alwasys a layer of resin sitting on the older faring when sanded back which creates sadi hard spot, q cell is the equivalent of microballons and is so fine it has the properties of a liquid
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Old 08-01-2007, 11:31   #4
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So are you using the Silica as well???
The mixed consistancy should be about peanut butter. In other words, you want it to stay put, but you don't want it too dry. The epoxy is what gives it strength remember. If you can handle it and not get your hands wet with epoxy, it is too dry. YOU NEED GLOVES and the mix needs to be trowled on.
I don't really know what is causing your problem though.
Umm, if this helps. You need to fully prepare each layer. So you trowel on and allow to harden, but don't allow it to go too hard. Over night is all it needs. Try not to allow the older resin to go off too far as well. As the epoxy cures, the stuff goes harder and harder and after a week it is very hard. This may be one source of your problem.
When you fair, you use a long board. This allows you to take off the tops of surfaces and maintain the flat surface you are after. You take off JUST enough to do the job. If you are cutting down into older fairing, then you are going too far, or not far enough when you were fairing that older original layer.
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Old 08-01-2007, 11:44   #5
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Sean what manufacturer product are you using? I may know the product better than the name you are using.
But in general, "glue" powder which is the silica is White, extremely light and fluffy and has that "liquid" flow. It can be used for filling, but goes very hard and is difficult to sand. I would not recomend fairing with it.
Microspheres for fairing are a "tan" coloured material. Also extrememly light, but you can clump it with you hand. Much easier to sand, but as I said, it is for above waterline application.
Microballoons are a chocolate brown. Extremely light weight. The stuff weighs almost nothing. Very easy to sand and great for below waterline.
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Old 08-01-2007, 15:13   #6
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i have been laying the glass down then when the glas has gone green trowelling on a layer of bog, the problem comes that occasionally after sanding it back youll find the odd hollow, when you fill these hollows with qcell and sand it back there is a layer of resin sitting on the older bog which gives me the aforementioned fairing problem, q cell is a hollow microsphere
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Old 08-01-2007, 16:23   #7
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also how long does glass stay freen for generally?, i have been using 6-8 hr intervals but how long can you leave it for?
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Old 08-01-2007, 16:35   #8
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QCELL is the actual brand name . boatbuilders in Oz have been using the stuff for years.

Sean can I suggest that you need a bit mor resin in the mix. It's just one of those thing's where it pays off to use a bit extra.

We aim for more of a mayonaise mix, easy to spread yet won't slump. What we do is find the low's before hand and mark with a builders pencil or chalk .

Then you can pull some bog through these areas first, let them kick and then pull a screed over the lot..

By using the softer brew of bog, it allows you to feather off the edges to make the next screed easier to apply.

Me and a mate who actually likes fairing have got our skills up enough to be able to get to 80% finish using Hitachi sat180 two speed sander to fair the boat with 36 grit paper. We also have Tellesh sander .:: Telesch ::. - F8 which is a geat tool for the final bit using 60 grit.

If you are at the final stage of bogging and just trying to get that last little bit, we then go to highbuild.

We use AMERON coatings for highbuild and topcoat. Much more affordable than Sterling and Awlgrip and in my opinion a better product.
With the highbuild we mix in QCELLS as well and have been told you can get in around 30%, but I stick to around 20% and add a bit of paint tint just to give it a bit of colour.

You now have effectively a poor mans spray bog, which can then be boarded down very easily and evenly. while spraying you should see any lows that may be left, give these areas a few more coat's and the bit of paint thats left over when it starts to kick, wipe the left overs into those low spots if they need a bit more. Also fill any bad pinhole patches if you can .

After it's all boarded back,we use 60-80grit, spray with unmodified white primer, and when you sand you can then stop when some of the colour starts to show.

I've never gone any finer than 180 grit for the final sand before gloss.

Hope this help's

Dave
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Old 08-01-2007, 16:42   #9
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Quote:
Originally Posted by cat man do
With the highbuild we mix in QCELLS as well and have been told you can get in around 30%, but I stick to around 20% and add a bit of paint tint just to give it a bit of colour.

You now have effectively a poor mans spray bog
Are you actually spraying that on Dave? If so, what size nozzel on your gun? Do you have to bump up the pressure any? Have you ever colored your base coat darker to use it as a guide coat for finding those nasty low spots?

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Old 08-01-2007, 17:05   #10
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Hi rick, i've gone right off using compressors for spraying and now use airless spray gear. reason being is they are increadably fast, we put 80 litres on the hulls in about 4 hours, and it all goes where you point, not up in the air

I'm lucky enough that a mate has let me use a big jobby that is on wheels and the paint pickup drops into the 20 litre drum that the paint comes in, like the pic below.

This thing pump's just about anything and I leave it up to the local GRACO dealer to advise on which nozzle to use.

And yes, I always put different colours down for base coats and even wipe the hull with a bit of tint in metho before sanding to show stuff up.

Dave
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Old 08-01-2007, 19:10   #11
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Sean, I agree with Dave, it sounds like your'e making the mix too dry. I've found when it's that dry it can be hard to get an even mix - it kind of forms clumps in the tub which the mixer doesn't easily break up, and these might be the reason for the hard and soft spots you are finding when you sand.

More resin will make the sanding a bit harder though, but you'll get a more even result.
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Old 08-01-2007, 19:25   #12
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More resin will make the sanding a bit harder though, but you'll get a more even result.
Only a little bit, and road base [36 grit] sort's it out

Dave
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Old 08-01-2007, 22:02   #13
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so when you mix qcell into your high build thge 20% is that by volume or what?
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Old 08-01-2007, 23:24   #14
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I really just mix it in to a consistancy that i'd reckon you could get through the gun in it's thinned state.

We just got told 30% by a few pro's and we just kept tipping it in and mixing. On the last boat we had a pro show us the consistency and this time we just went a bit less as the airless lines are about 50ft long and I didnt want to have a tough job cleaning them out if I had added too much.

I don't think there is an exact science, but I know it work's and cost's a fraction of the U.S Paint's version.

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Old 09-01-2007, 02:04   #15
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how long is it before glass is no longer green
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